<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <p id="asd"></p>
</body>
</html>
<script>
    function fn(){
        var num = document.querySelector('#asd')
        for(var i = 60;i >= 0;i--){
            num.innerText = i
        }
    }
    function fn2(){
        var num = document.querySelector('#asd')
        time = setInterval(function(){
            for(var i = 60;i >= 0;i--){
            num.innerText = i
        }
        },1000)
    }
    function fn3(){
        var num = document.querySelector('#asd')
        var arr = new Date()
            arr2 = new Date("2300/8/8")
        var time = arr2 - arr
        var time1 = Math.floor(time /(1000 *60) % 60)
        var time2 = Math.floor(time /1000 % 60)
        return time1 + '分' + time2
    }
    var num = document.querySelector('#asd')

    setInterval(function(){
        num.innerHTML = fn3()
    },1000)
</script>